The present invention relates to a signal generator which generates signals in a semiconductor device by utilizing a charged particle beam and to a method of generating signals using the same.
The prior art of this kind has been disclosed in, for example, U.S. Pat. No. 3,531,716. According to this prior art as shown in FIG. 2, reverse bias characteristic of pn junction of a semiconductor is utilized to generate a voltage signal on a metallic electrode 102 connected to a p-type region 101 provided in an n-type region 104 by irradiating the metallic electrode 102 with an electron beam 103. The specification of the above U.S. patent further describes a method in which a supply terminal of a semiconductor circuit is irradiated with the electron beam and the circuit is operated with the beam current as a source of current. Another prior art can be found in the Journal of Vacuum Science and Technology, 19, 1981, pp. 1010-1013 according to which, as shown in FIG. 3, the pn junction of a diode element 201 is irradiated with an electron beam 202 to operate a flip-flop circuit 203. Namely, a high-speed switching operation is realized by utilizing the function of current amplification in the pn junction portion despite the beam current is small.
The prior art shown in FIG. 2 can be evaluated for its idea and method for generating voltage signals in the device upon irradiation with an electron beam. There, however, is left a problem in that since a beam current of an irradiated charged particle beam is converted directly into a voltage signal through a load device, an extended period of time is required for generating a signal when a beam current of a weak focused beam is used, and a circuit in the latter stage must have a very high impedance. The prior art shown in FIG. 3 is excellent in that the current is amplified through the input stage on which a probe beam is incident, solving the problem inherent in the prior art of FIG. 2. However, since the pn junction portion must be irradiated with a beam, the probe point (beam irradiation position) is limited to a place where a diode can be formed. Further, when the probe beam that is used consists of an ion beam, the pn junction portion of the diode element is broken down by the sputtering which makes it impossible to use this circuit setup.